Paper web formation using dual fabrics

ABSTRACT

TO FORM A WEB OF PAPERMAKING FIBERS IN THE PROCESS OF PAPERMAKING. A SUSPENSION OF SUCH FIBERS IS PASSED FROM A HEAD BOX BETWEEN A PAIR OF ENDLESS FABRICS, AT LEAST ONE OF WHICH IS A FORAMINOUS FORMING CARRIER. THE FABRICS ARE MOVED OVER PATHS THAT ARE SUBSTANTIALLY PARALLEL OVER A SUBSTANTIAL DISTANCE TO AND INCLUDING THE OUTLET ORIFICE OF THE HEAD BOX AND ARE SPACED A PREDETERMINED DISTANCES APART. PRIOR TO ANY SUBSTANTIAL FORMATION OF A WEB, THE SUSPENSION LEAVES THE ORIFICE ENTRANINED   BETWEEN THE FABRICS AND MOVES AT THE SAME SPEED AND IN THE SAME DIRECTION. THEREAFTER A WEB OF THE PAPERMAKING FIBERS IS FORMED BY REMOVING WATER FROM THE SUSPENSION THROUGH THE FORMING CARRIER WITHOUT EXERTING SUBSTANTIAL SHEAT FORCES UPON THE FORMING WEB.

July 3, 1973 G. T. WARD 3,743,571

PAPER WEB FORMATION USING DUAL FABRICS Original Filed Feb. 5, 1969 3 Sheets-Sheet 1 I' v u .l II/ ///,////////////////////////W////:r////.mmm 'NVENTOE GEORGE T. WARD ATTOENEYS July 3, 1973 5.1. WARD PAPEH WEB FORMATION USING DUAL FABRICS Original Filed Feb. 3, 1969 3 Sheets-Sheet 2 !NVENTOE GEORGE T. WARD ATTOENEYS July 3, 1973 G. T. WARD PAPER WEB FORMATION USING DUAL FABRICS 3 Shee*.s-Sheet 5 Original Filed Feb. 3. 1969 mm w nw ATTOIZNCY5 United States Patent O U.S. Cl. 162-203 7 Claims ABSTRACT OF THE DISCLOSURE To form a web of papermaking fibers in the process of papermaking, a suspension of such fibers is passed from a head box between a pair of endless fabrics, at least one of which is a foraminous forming carrier. The fabrics are moved over paths that are substantially parallel over a substantial distance to and including the outlet orifice of the head box and are spaced a predetermined distance apart. Prior to any substantial formation of a web, the suspension leaves the orifice entrained between the fabrics and moves at the same speed and in the same direction. Thereafter a web of the papermaking fibers is formed by removing water from the suspension through the forming carrier without exerting substantial shear forces upon the forming web.

This application is a division of copending application Ser. No. 796,l31, filed Feb. 3, 1969, IlOW Pat. No. 3,645,842.

This invention relates generally to methods for making paper. 'More specifically, the invention relates to a method of forrning a web of papermaking fibers. The invention is particularly directed to the control of the suspension of papermaking fibers as it passes from the head box to the forming region.

In papermaking an aqueous suspension of papermaking fibers, known as stock, is supplied to a chamber, known as a head box. From the head box the stock flows through an orifice, commonly known as a slice, and pours onto a moving endless forming carrier, commonly known as a wire. Water is drained from the suspension through the forming carrier, forming a web of the papermaking fibers on the carrier, the web being subsequently dried to form paper.

Certain non-uniformity of the finished paper, particularly in high speed Operations, may be occasioned by aberrations in the free surface of the stock as it is moved along on the carrier into the region where the paper web is formed. Such aberrations are carried on through the machine and appear in the finished paper. It has therefore proved desirable to control the free surface of the stock on the carrier. It is known to utilize a so-called twin wire machine wherein the stock is directed from the head box as a free jet into a space between a pair of endless forming carriers. The turbulence in the exposed surface of the jet between the head box and carriers .nevertheless permits certain non-uniformity in the surface of the stock as it is deposited between the carriers, again producing aberrations in the paper.

It is also known to utilize a pressure forming machine wherein the forming carrier passes over a large opening at the outlet of. the head box, and the stock is forced against the carrier under pressure. The water is drained from the stock in this pressure forming region to form a web on the carrier. Such systems have also included the use of a felt carrier passing into the head box and overlaying the formed web as it leaves the head box.

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Although in such apparatus there is no uncontrolled free surface of the stock on the forming carrier, the stock 'in the head box is turbulent. This condition produced great shear forces that may interfere with the orderly formation of the web, resulting in non-uniformity.

In accordance with the present invention, the web is formed while keeping the stock controlled at all times from the head box to the web forming region. There is no free surface of stock on the forming carrier until the stock has been metered out onto the forming carrier with all parts of the stock moving unifornly at the speed of the forming carrier and in the same direction. Further the movement of all of the stock at the speed of the forming carrier is achieved prior to any substantial formation of the web. To this end the stock in the head box is entrained between a pair of endless fabrics moving at the same speed. The fabrics are moved parallel to one another over a relatively long distance so that any great turbulence or speed differentials in the stock entrained between the fabrics are damped and dissipated until the stock all moves with the fabrics without turbulence. The fabrics carry the entrained stock out of the head box to the web forming region, no substantial formation of the web being effected until all of the entrained stock is moving uniformly in the direction of the fabrics. Under these conditions, there are no substantial shear forces on the web as it is formed on one of the carriers.

It is, therefore, an object of the present invention to provide an improved manner of forming a paper web wherein the stock is controlled at all times from its exit from the head box to its formation into the web. Another object of the invention is to provide apparatus for controlling the flow of stock to the formation region. Other objects and advantages of the invention will become apparent from the following detaled description, particularly when taken with reference to the drawings in which:

FIG. 1 is an illustration, partly diagrammatic and partly in section, showing a papermaking machine incorporating the present invention;

FIG. 2 is an enlarged sectional view of the head box of the apparatus shown in FIG. 1;

FIG. 3 is an enlarged sectional view of a modified form of the bottom plate. of the head box shown in FIG. 2;

FIG. 4 is a diagrammatic illustration of another form of papermaking machine incorporating a modified form of the present invention;

FIG. 5 is an enlarged sectional view of the head box of the apparatus shown in FIG. 4;

FIG. 6 is a diagrammatic illustration of a modification of the form of the invention shown in FIG. 4; and

FIG. 7 is an enlarged sectional View of the head box of the apparatus shown in FIG. 6.

In FIGS. 1 and 2 there is illustrated a papermaking machine including a head box 10 fashioned in accordance With the present invention. A distribution system 12 is at the inlet of the head box 10, as illustrated. The head box 10 comprises an upwardly slantng rectangular channel portion 14 at its inlet end. The interior of the channeled portion 14 contains' a plurality of relatively small, straight tubes 16 disposed parallel to the longitudinal axis of the channel 14. The tubes may be hexagonal in cross section so as to fill the channel portion 14 in honey-comb fashion. An endless fabric 18 is directed about a breast roll 20 into the head box 10 and out through an outlet orifice 22. The fabric 18 may be a conventional forming carrier or wire. A second endless fabric 24 also enters the head box 10 after passing around a roll 26. The fabric 24 also passes through the head box 10 and out the outlet orifice In operation an aqueous suspension 23 of papermaking fibers is supplied to the head box from the distribution system 12. The distribution system 12 Supplies the suspension over the entire width of the head box which is substantially the same width as the endless fabric 24. The suspension of papermaking fibers flows through the tubes 16 into the central part of the head box 10.

The head box 10 may be of the pressure type in which means (not illustrated) is provided for maintaining air pressure in that portion of the head box 10 above the flowing fiber suspension 23. Means (not illustrated) maintains the suspension 13 at the desired level. The head box 10 may at the same time be of the frozen flow type. Frozen or plug flow is characterized by a thin shear zone adjacent to any surface of the head box in contact with the stock, in which zone the fibers tend to roll or shear past one another, while the rest of the flowing suspension appears to be frozen into a solid plug moving With uniform velocity throughout its cross section. Frozen flow may be initiated by the tubes 16, which are made so long that the flow therein is stabilized.

Frozen flow reduces turbulence in the stock that distnrbs the uniform formation of a paper web and at the same time reduces occng of the fibers, for with little or no movement of the fibers in relation to one another within a frozen tflow, the gathering together of the fibers into flocs takes place very slowly or not at all. Floccing is undesirable because any fioc pattern may be retained in the finished paper. Should Operating conditions produce flocs of objectionably large size, a rod roll 28 may be rotated within the head box 10 to provide appropriate turbulence and defioccing of the fibers.

The suspension 23 moves out of the head box 10 through the outlet orifice 22. The suspension is carried between the fabrics 18 and 24 to a forming region. In the forming region a forming board 30 drains water from the suspension 23 to form a web 31 of papermaking fibers on the forming carrier 18. The web then may be carried over de-watering means such as foils 32 or suction boxes 34 or both, as illustrated in FIG. 1. Alternatively, or in addition, the de-Watering means may include table rolls or drainage elements as disclosed in Lee U.S. Pat. No. 3,332,838. The de-watering means extracts further water from the wet web 31. The web 31 may be removed from the fabric '18 at a conch roll 36 and transferred to a press felt 38. The press felt 38 carries the Web through a press section 40 where further water is pressed from the web 31. The web is then carried to a dryer section 42 which dries further water from the web until it reaches the desired dryness. The dried web is removed from the dryer by a doctor blade 44. I

The head box 10 illustrated in FIG. 1 is shown in greater detail in FIG. 2. FIG. 2 illustrates more specifically the paths taken by the fabrics 18 and 24 through the head box 10. The lower fabric 18 enters the head box 10 at the breast roll 20. The breast roll 20 is disposed beneath an apron 46, and the fabric 18 enters the head box 10 between the apron 46 and a bottom plate 48 which forms part of the bottom of the head box. The bottom plate is preferably flat and horizontal, and the fabric 18 moves along the upper surface of the plate 48 to the outlet orifice 22. The fabric 24 enters the head box 10 between a seal 50 and an upper plate 52 constituting the top of the head box 10. The fabric 24 moves along the under surface of the plate 52 to the orifice 22.

The plates 48 and 52 constitute two of the walls of the head box 10 and, as illustrated in FIG. 2, the facing surfaces of the plates 48 and 52 are substantially parallel in a region 54 extending over a rather substantial distance up to the outlet orifice 22. They are spaced a constant predetermined distance apat over this entire region up to and including this outlet orifice 22. The fabrics 18 and 24 enter the head box 10 at points where the cross section of the flow of the suspension through the head box 10 is many times greater than the cross section of the outlet 4. orifice 22. At these points of entry the rate of flow of the stock 23 is relatively low, for example, between about 0.5 feet per second and about 5 feet per second.

The fabrics 18 and 24, being guided by plates 48 and 52, respectively, efl'ectively form moving walls of the head box 10. These moving walls are directed by the shapes of the plates to converge gradually with the stock therebetween. Because of the convergence of the flow, the stock moves at a much faster rate in the region 54 than the rate at which it was moving at the points where the fabrics entered the head box 10. The fabrics 18 and 24 may be of the order of A inch to 3 or 4 inches apart in the region 54, depending on basis weight of paper being manufactured and the consistency of the stock 23. I

The pressure in the head box 10 and the spacing of the plates 48 and 52 in the region 54 principally determine the rate of flow of the stock 23 from the head box 10. The fabrcs 18 and 24 are driven at a linear velocity substantially matching the velocity of the stock 23 in the region 54. Under such conditions the fabrics 18 and 24 substantially entrain the stock 23 in this region; that is, the fabrics 18 and 24 and the stock 23 disposed therebetween all move at the same speed and in the same direction in the parallel region 54. Any tendency of any part of the entrained stock to move faster or slower than the fabrics 18 and 24 is overcome by removing or adding energy to the suspension by means of the fabrics 18 and 24. The parallel region 54 is made relatively long, -for example, from 1 to 10 feet, depending upon the linear velocity of fabrics 18 and 24 and their spacing. The length of the region 54 is such as to permit all parts of the stock 23 entrained between the fabrics 18 and 24 to move at the matching speed of the fabrics.

With all of the suspension moving at the speed of the fabrics, the suspension may be said to be completely controlled. There is no gross turbulence to disrupt the formation of the forming web with all of the suspension moving at the same velocity. Water may then be drained from the suspension without producing shear forces which would disrupt the web 31 as it forms. Therefore, in accordance with the present invention, substantially no formation of the web is permitted until all of the suspension of fibers is moving at the proper velocity.

To preclude any formation of the web 31 prior to complete control of the stock 23, the lower part plate 48 may be made substantially impervious, as shown. Actually it is often preferred that there be some small drainage of water prior to the orifice 22 to form a thin film of fibers upon the fabric 18 prior to the principal web formation. This preliminary formation is done gently so that the incompletely controlled stock does not disrupt the forming web. In order that there may be small drainage through the carrier 18 within the head box 10, the bottom plate 48 may be made slightly water pervious as by making small holes 55 through the plate 48, as shown in FIG. 3.

After the stock 23 and the fabrics 18 and 24 are moving together at the linear speed of the fabrics, the stock is carried out of the head box 10 through the outlet orifice 22. The stock 23 is carried through the orifice 22 entrained between the fabrics 18 and 24, which are still moving parallel to each other. The suspension is thus carried to the forming board 30 where the principal formation of the web occurs. At this point, the fabric 24 may be passed around a roll 56 and directed away from the forming web 31. The fabric 24 may pass around additional rolls 58 to roll 26.

After the web 31 has formed, it may be processed in a conventional manner. It may be de-watered by the foils 32, the suction box 34, and the press section 40, and then dried in the dryer section 42. The fabric 18 may be returned from the conch roll 36 to the breast roll 20 over a roll 60. The press section 40 may include press rolls 62 and a roll 64 over which the press felt 38 travels. The dryer section 42 may include a dryer drum 66.

Various modications may be made in the apparatus within the scope of the invention. For example, the upper fabric 24 may be directed along the top of the web 31 over a greater portion of its travel, rather than being taken from the web directly after it leaves the outlet orifice 22. Indeed, the fabrics 18 and 24 may be made of material which may be carried on through the press section 40. Maintaining the second fabric 24 against the web 31 permits the formation of the web 31 on a forming carrier running other than generally horizontal. Further, the second fabric `24 may itself be a forming carrier, and water may be removed from both sides of the web. Such apparatus is illustrated in FIGS. 4 and 5, which also illustrate a somewhat different type of head box 10.

As shown in FIG. 4, a distribution system 68 Supplies the suspension 23 of papermaking fibers vertically into a head box 70. The suspension exits from the head box 70 through an outlet orifice 72 between first and second forming fabrics 74 and 76. The suspension 23 is then carried between the fabrics 74 and 76 to forming boards 78 and 80. In this region a web 31 of papermak'ng fibers is formed between the fabrics 74 and 76. Water may then be extracted from -both sides of the web through the fabrics 74 and 76 using such conventional means as foils 82, a suction roll 84, and suction boxes 86. The forming fabrics are of the type that may be passed through a press section 88 comprising press rolls 90 and may therefore be used to carry the web 31 through the press section. The web may then be carried to a dryer 92 which dres the web to form paper. Paper may be taken oli? the dryer 92 by a doctor bade 94. After the web 31 is taken off at the dryer 92, the forming fabric 74 may return about rolls 96 to a breast roll 98, whence it enters the head box 70. Similarly the forming fabric 76 returns about rolls 100 to a breast roll 102, whence it, too, enters the head box 70. The removal of water from the formed web may be entirely conventional. It is the conditioning of the stock suspension for formation of the web that is the object of the present invention.

As shown in greater detail in FIG. 5, the flow of stock 23 through the head box 70 may be generally vertical up to the points where the fabrics 74 and 76 enter the head box 70. The fabric 74 enters the head box 70 between an apron 104 and a plate 106. Similarly, the fabric 76 enters the head box 70 between an apron 108 and -a plate 110. The plates 106 and 110 form Walls of the head box 70. As illustrated in FIG. 5, the fabrics 74 and 76 enter the head box 70 at points where the plates 108 and 110 are relatively widely spaced and, therefore, where the rate of flow of the suspension of papermaking fibers is relatively slow. The facing surfaces of the plates 108 and 110 gradually converge until they reach a predetermined separation at region 112, in which region the facing surfaces are substantially parallel. This region 112 extends up to and including the outlet orifice 72.

Just as in the case of the apparatus of FIGS. 1 and 2, the apparatus of FIGS. 4 and 5 provides for entraining of the suspension 23 between the fabrics 74 and 76 over a substantial distance during which the suspended fibers and the water they are suspended in are moving at the -velocity of the carriers 74 and 76 and in the same direction. As with the form of the invention illustrated in FIGS. 1 and 2, the apparatus of FIGS. 4 and 5 conditions the suspension 23 so that the web 31 may be formed without exerting substantial shear forces upon the forming web.

The apparatus of FIGS. 4 and 5 may be used for the same purposes as the apparatus of FIGS. 1 and 2. The respective head boxes 70 and may be used in the same way. The head box 70 of the apparatus of FIGS. 4 and 5 may be used with de-Watering and drying systems as shown in FIGS. 1 and 2. Modifications such as these may be made without departing from the scope of the invention, which is limited only by the claims.

A further modification of the invention is shown in FIGS. 6 and 7. With this form of the invention, it is possible to make multi-layered paper. In previous machines for making multi-layered paper, one layer is laid and dewatered, and then a second layer is laid upon the first and dewatered. The intervening dewatering of the first layer results in marked weakness between the layers, making delamination likely. In accordance with the modification of the invention illustrated in FIGS. 6 and 7, all layers are laid and dewatered simultaneously, making a laminated web with the laminates closely adherent and intertwined at their interfaces.

The apparatus for making mu'lti-layered paper may be substantially like the apparatus shown in FIGS. 4 and 5, except that in the apparatus as illustrated in FIGS. 6 and 7 a second distribution system 168 Supplies a second suspension 123 through a separate inlet 125 into the head box 70. As shown, the second suspension 123 is delivered in a layer between two layers of the first suspension 23. The multi-layered stock may then be processed as a single unit in the manner described above for a single layer in connection with the apparatus shown in FIGS. 4 and 5, resulting in 'a three-layered paper. Two-layered paper may be made by introducing the second suspension 123 on one side of the first suspension 23, rather than centrally thereof. Other layered arrangements may be made by variations in the distribution systems and their number and in the disposition of the respective inlets to the head box.

The multi-layered paper may be formed of layers of fibers 'having different desired characteristics. For example, the outer layers may be made from wood pulp and the inner layer of synthetic fibers. In this connection it should be noted that the term paper as used herein is not limited to webs made from any particular fibers.

What is claimed is:

1. In a method of making paper, the forming of a web of papermaking fibers by the steps comprising passing a suspension of papermaking fibers into a chamber having an outlet; passing a pair of endless fabrics at the same speed as each other continuously into said chamber, at least one of said fabrics being a foraminous forming carrier; entraining suspended papermaking fibers between said fabrics and moving the suspended fibers uniformly in speed and direction toward said outlet substantially completely blocking off the endless fabrics against drainage prior to the outlet; passing said fabrics with the entrained uniformly moving suspension out of said outlet prior to any substantial formation of a web; and thereafter forming a web of papermaking fibers on said forming carrier by removing fluid from said suspension through said carrier.

2. The method of claim 1, wherein said suspended papermaking fibers are entrained between said fabrics and moved at the speed thereof by directing said fabrics along paths that are substantially parallel to each other over a substantial distance to and including said outlet and spaced a predetermined distance apart.

3. The method of claim 1, wherein substantially all of said suspension fiowing from said outlet is that entrained between said fabrics.

4. The method of claim 1 wherein said fabrics are passed into said chamber at points where the suspension is moving more slowly than said fabrics and thereafter are moved along gradually converging paths to the point where their paths are substantially parallel.

5. The method of claim 1 wherein a film of papermaking fibers is formed on said forming carrier prior to its exit through said outlet.

6. The method of claim 1 wherein both fabrics of said pair of fabrics are foraminous forming carriers and said web is formed by removing water through both of said fabrics.

7 7. The method according to claim 1 wherein a plurality of suspensions are passed into said chamber in layers and are processed together to form a layered web.

References Cited UNITED STATES PATENTS 8/1932 Mason 162-203 X 8 3,440,136 4/ 1969 Nelson et al. 162-203 X 2,977,277 3/ 1961 Kelly 162--203 3,645,842 2/ 1972 Ward 162-303 ROBERT L. LUNDSAY, JR., Primary Examine' A. DANDREA, JR., Assistant Examiner 

